Path: utzoo!attcan!uunet!mcsun!unido!mpirbn!p554mve
From: p554mve@mpirbn.mpifr-bonn.mpg.de (Michael van Elst)
Newsgroups: comp.arch
Subject: Re: harvard architectures
Message-ID: <1328@mpirbn.mpifr-bonn.mpg.de>
Date: 21 Oct 90 22:48:34 GMT
References: <9010160322.AA13808@lilac.berkeley.edu> <3468@bnr-rsc.UUCP> <7883@darkstar.ucsc.edu> <2773@crdos1.crd.ge.COM> <1320@mpirbn.mpifr-bonn.mpg.de> <2777@crdos1.crd.ge.COM>
Reply-To: p554mve@mpirbn.UUCP (Michael van Elst)
Organization: Max-Planck-Institut fuer Radioastronomie, Bonn
Lines: 17

In article <2777@crdos1.crd.ge.COM> davidsen@crdos1.crd.ge.com (bill davidsen) writes:
>In article <1320@mpirbn.mpifr-bonn.mpg.de> p554mve@mpirbn.UUCP (Michael van Elst) writes:
>| You have to decode the opcode byte to guess the size of the instruction.
>
>  Simple opcodes, only 256 and you could determine the length of the
>instruction from it (may not be true of Z80, don't know).

The Z80 has some 'prefix' opcodes. Some of the activated the index registers
(which might add a displacement byte to the instruction), and some of them
switch to another instruction table. There were combinations of these too.

Regards,
-- 
Michael van Elst
UUCP:     universe!local-cluster!milky-way!sol!earth!uunet!unido!mpirbn!p554mve
Internet: p554mve@mpirbn.mpifr-bonn.mpg.de
                                "A potential Snark may lurk in every tree."